The procession of mourners began overnight, with a single candle and a yellow flower.

By Tuesday morning, they came one after another, leaving bouquets, balloons, and stuffed animals on the front porch of the empty house. More than a thousand gathered with candles at a Dorchester playground in the evening, and on the Internet, prayers and expressions of grief came from around the world for 8-year-old Martin Richard, killed in the same ­instant his mother and sister were ­severely injured.

In the frenetic social media traffic that followed the Marathon blasts, a photograph of the wide-eyed boy holding a hand-lettered sign — “No more hurting people. Peace” — ­became an international emblem of the the day’s horror.

The boy’s father, Bill Richard, a loved and respected figure in his neighborhood, was with his family when the bomb detonated. He survived with shrapnel damage to his legs.

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“My dear son Martin has died from injuries sustained in the attack on Boston,” Bill Richard said in a statement Tuesday. “My wife and daughter are both recovering from serious injuries. We thank our family and friends, those we know and those we have never met, for their thoughts and prayers. I ask that you continue to pray for my family as we remember Martin.”

As was true for so many of the injured, the family had gone to the race to celebrate the dawn of warm weather and one of Boston’s most cherished events.

The family watched the first part of the race near Hereford Street, several blocks away from Copley Square, according to a family friend. They were keeping watch for friends from their close-knit neighborhood, several of whom were running the race on Monday for charity.

They took a break for ice cream. When they returned around 2:30 p.m., they decided to watch from a spot nearer the finish line, where Martin and his siblings could see the weary runners take their last triumphant steps. Fifteen minutes later, the explosion rocked the sidewalk.

News spread fast in the Ashmont section of Dorchester, and on Tuesday, some children from Martin Richard’s class at the Neighborhood House Charter School in Dorchester came to the front porch.

Classmates said Martin told a mean knock-knock joke, ­always won at math games, and stuck up for friends at school.

“If somebody was left out, he would come say, ‘Want to join my group?’ ” said Colin Baker, 9. “He sticks up for kids.”

“It should not have happened to him,” Colin said. “It should not have happened to nobody.”

Martin’s 7-year-old sister, Jane looked up to her big brother, another friend said. “She likes playing like Martin,” said Kaytlyn Lynch, 8. “She’s just like Martin.”

The family was better known than most in the city. Bill Richard, a respected longtime activist in Dorchester, pushed for the rehabilitation of the Ashmont T station and was intimately involved in improv­ing the neighborhood in recent years, friends said.

His wife, Denise, who works as a librarian at her son’s school, is a leader of the local civic association.

Hundreds of their friends and neighbors, already stunned by the bombings, were stunned again by the gut-wrenching revelation that they knew the devastated family.

When Dotty Willett heard an 8-year-old was killed, she said she felt overwhelmed, imagining the family’s pain.

“Then I found out we were the family,” said Willett, her voice choked with emotion.

Martin Richard was her cousin’s son, she said.

Many could not bring themselves to talk about the loss.

“It’s too emotional, and it’s a very private thing,” said Judy Tuttle, a leader of the Ashmont Adams Neighborhood Association, her voice shaking. “I just ask that people be patient.”

Former state senator Jack Hart, a longtime friend, called the Richards “pillars of the community . . . a model family, who somehow always found the time to give something back.”

“Any tragedy of this sort is extraordinarily difficult, but when you know people, when it’s people in your life, in your school, that’s when it really hits home,” said Hart.

The sidewalk in front of the family’s home was bright with chalk drawings Tuesday morning, butterflies, flowers, and stars that a neighbor said the Richard children made on Sunday night. The chalk sat in an open bucket by a hedge where the children had left it.

Neighbor Dan Aguilar said he had barely slept the night before because he could not stop thinking about the family. “That little boy will never come home again,” he said.

Emira Myers, 10, came with her mother to the family’s home, where she left a small stuffed animal on the porch. She went to school with ­Martin, she said, though they were not in the same class.

Asked how she was feeling, the girl said, “Scared.”

“I never know where they are,” she added.

“Where the bad people are,” her mother murmured, and Emira nodded.

A few blocks away, the black clock in the center of ­Peabody Square was wrapped in black bunting, stopped at 2:50, when the bombs went off.

Close by, a man with an ­accordion played a mournful rendition of “Amazing Grace.”

He said he played Tuesday outside the John Hancock building, but left to come home to Dorchester to play in honor of the Richard family.

“Tears my heart out,” said the man, who declined to give his name. “The city’s never ­going to be the same.”